Directional radio receiver



M r h 1943. H. c. FORBES 2,313, 1

DIRECTIONAL RADIO RECEIVER Original Filed Aug. 28, 1940 INVENTOR #f/VEK C F0255? ATTORNEY Patented Mar. 9, 1943 UNHTED STTE DIRECTIONAL RADIO RECEIVER Henry C. Forbes, Eggertsville, N. Y., assignor to Colonial Radio Corporation, Bufialo, N. Y.

5 Claims. (01. 250-20) This invention relates to radio receiving apparatus and more particularly to radio receiving apparatus equipped with loop antennas and is a division of my application Serial No. 354,539, filed August 28, 1940, now Patent No. 2,266,630. It has great utility in radio receivers of the socalled table model type intended particularly for broadcast listeners, but it will be understood that my invention is not limited thereto and is capable of use in other types of radio receivers and for other purposes, particularly where it is desirable to obtain the directional characteristics of a rotatable loop where it is undesirable or impractical to rotate the loop.

It is known that reception may be had from loop antennas as well as from other types of antennas, and it is known that loop antennas have a directional characteristic, the pick-up being a maximum when the plane of the loop is in the line of the incoming signal and a minimum when it is at right angles thereto.

In recent years, it has become customary to equip broadcast receivers with built-in loops. In some cases, the loop has been fixedly mounted in the receiver, so that its direction could not be changed except by moving the receiver. In other cases, arrangements have been provided by means of which it was possible to rotate the loop through a limited amount within the receiver.

Neither of these arrangements has proved satisfactory for broadcast listeners as a whole. In the first case, that is where the loop is fixed in position in the receiver, it is obviously impractical for the listener to move the entire receiver to be sure that in each case the loop is set in the proper direction for maximum signal, or for minimum interference.

In the second case, that is where the loop is arranged for rotation in the receiver, in some instances it has been necessary to move the receiver in order to get at the loop to rotate it, and in other instances, mechanism has been provided having a control on the front or some other accessible part of the receiver by means of-which the listener might rotate the loop. Such arrangements have tended to be unduly expensive because of the space requirements for the rotatable loop and because of the'complexity of the mechanism required to rotate it; and even where such apparatus is provided it is not easy for the layman to find the particular angle of the loop for best results, and in any case such apparatus has not been possible for installation in so-called table model receivers where the space requirements are such that it is not possible to provide a rotatable loop.

Among the objects of my invention are to provide a loop installation which is easily assembled in table models Without requiring any substantial amount of space and by means of which the lay operator may easily take advantage of the directional characteristics of the loop without moving the receiver itself and without the employment of complicated or expensive mechanisms.

A further object of my invention is to provide apparatus of the class described which may be readily installed in table model receivers and which may be operated by a simple control to vary the directional characteristic of the loop installation.

Still other objects and advantages of my invention will be apparent from the specification.

In this application I have particularly pointed out and distinctly claimed the part, improvement or combination which I claim as my invention or discovery, and I have explained the principles thereof and the best mode in which I have contemplated applying those principles, so as to distinguish my invention from other inventions.

In the drawing:

Fig. 1 is a perspective View of a table model" receiver according to my invention; and

Fig. 2 is a circuit diagram of one form of circuit which may be employed, in accordance with my invention; and

Fig. 3 is a polar diagram of the response of the apparatus of Fig. 2.

Referring now more particularly to Figs. 1 and 2, I have shown in Fig. 1 one form of table model receiver, and in this instance I may provide within the housing of the receiver the two loops 1 and 2 mounted at right angles to each other and arranged in any convenient place within the cabinet. Both loops preferably have the same inductance and capacity, so that they may be interchanged in a tuned circuit without substantially afiecting its tuning. For example, the loop 'I may be arranged at the back and extending along the back, whereas loop 2 may be at one end and extending along the end.

If desired, the receiver may be a tuned radio frequency amplifier type instead of a superheterodyne, my invention not being concerned with the type of circuit employed other than as herein described and claimed.

Referring now to Fig. 3, it will be noted that if the dotted line circles Ir represent the response of loop I, then the dotted line circles 2r represent the response of the loop 2, each response curve being in the form of a figure 8, and the two figure 8s loeing disposed at 90 to each other. The overall response which may be obtained is indicated by the outside full line curve. Actually this curve should be superimposed upon the dotted lines adjacent to it, but for purposes of clarity, it has been slightly separated therefrom. By inspection of Fig. 3, it will be noted that no matter from what direction the incoming signal may come, by switching from one loop to the other, it is always possible to get a response which is between the response which would be obtained if the loop pointed directly in with the signal and a minimum of 0.707 of that value, this because it is always possible by operating the control 8 as will be described, in a manner to select the loop which is no more than 45 out of line with the desired signal.

In the circuit shown in Fig. 2, condenser M may be connected across loop and condenser 9 across loop 2, and one side of each of thesetuned circuits may be connected to the input circuits of amplifier tubes and 2| respectively, the output circuits of which are connected together and feed a common coupling circuit diagrammatically shown. The control electrode 202) of tube 20 may be connected to the common point of loop and condenser i4 and the control electrode 2|b to the common point of loop 2 and condenser 9. Preferably the inductance and capacity of circuit 4 are identical with those of circuit 29, so that no change of tuning occurs as between the two circuits, and condensers 9 and I4 may be ganged so that both circuits are always tuned to the same frequency.

' The circuit of Fig. 2 provides for a smooth and gradual change of the characteristic of loop I to the characteristic of loop 2.

Cathode 20a may be connected to one end of resistor 39a, shunted by condenser 23, for instance the top end, the other end of which may be grounded, and cathode 2|a may be connected to the lower end of resistor 30b, shunted by condenser 25, the upper end of which may be grounded. One side of condenser l4 may be connected to control electrode 2% of tube 2!) and the other side to contact 31a of slider 3|, while one side of condenser 9 may be connected to control electrode 2|a of tube 2|, and the other side to contact 3 lb of slider 3|. The biases are so chosen on tubes 20 and 2| that when the slider 3| is at the top end of resistor 3%], tube 2| is biased to cutoil, whereas tube 20 has its normal operating bias. By moving the slider 3| to the bottom extremity of resistor 39, tube 2| hasits normal operating bias and tube 2!] is biased to cut-off. For intermediate positions, an intermediate effect is obtained which is similar to what would be obtained if loop or 2 were rotated; that is to say, the directional pattern gradually and smoothly changes from that of loop to that of loop 2 and vice versa.

Knob: 8 may be arranged to operate slider 3| by rotation, and such operation will give either the directional characteristic of loop I alone or loop 2 alone, or the directional characteristic of an equivalent loop at any angular position intermediate the positions of loops and 2.

While I have shown and described certain preferred embodiments of my invention, it will be understood that modifications and changes a common terminal respectively;

may be made without departing from the spirit and scope of my invention as will be clear to those skilled in the art.

I claim:

1. A radio receiver comprising, in combination, a housing, a pair of vacuum tubes within said housing, each of said tubes having a cathode and a control electrode, said tubes having a common output circuit, a pair of loops mounted fixedly within said housing at angles to each other, a pair of impedances connected between said cathodes and a common terminal respectively, a connection from the free terminal of one of said loops to the control electrode of one of said tubes, a connection from the free terminal of the other of said loops to the control electrode of the other tube, and means for connecting the grid return side of said loops to said impedances respectively, said means serving to vary the said impedances between loops and said common terminal in an inverse manner.

2. A radio receiver comprising, in combination, a housing, a pair of vacuum tubes within said housing, each of said tubes having a cathode and a control electrode, said tubes having a commonv output circuit, a pair of loops mounted fixedly within said housing at angles to each other, a pairjof impedances connected between said cathodes and a common terminal respectively, a connection from the free terminal of one of said loops to the control electrode of one of said tubes, a connection from the free terminal of the other of said loops to the control electrode of the other tube, and connections from said loops to said impedances respectively, said connections being simultaneously variable in opposite senses.

3. In combination, a housing; radio receiving apparatus positioned within said housing, and comprising a pair of vacuum tubes, each of said tubes having a cathode and a control electrode, said tubes having a common output circuit; a pair of loops mounted fixedly within said housing at angles to each other; a pair of impedances connected between said cathodes and a common terminal respectively; a connection from the ,free terminal of one of said loops to the control electrode of one or said tubes; a connection from the free terrrnnal of the other of said loops to the control electrode of the other tube; means for connecting the grid return side of said loops to said impedances respectively, said means serving to vary the said impedances between said loops and said terminal in an inverse manner; and a tuning element connected to each of said loops, the constants of said tuning elements and of said loops being so related that each of said loops tunes alike; and a single control for operating both said tuning means.

i. In combination,,a housing; radio receiving apparatus positioned within said housing and comprising a pair of vacuum tubes, each of said tubes having a cathode and a control electrode, said tubes having a common output circuit; a pair of loops mounted fixedly within said housing at angles to each other; a pair of impedances connected between said cathodes and a a connection from the free terminal of one of said loops to the control electrode of one of said tubes; a connection from the free terminal of the other of said loops to the control electrode of the other tube; means for connecting the grid return side of said loops to said impedances respectively, said means serving to vary the said impedances between said loops and said terminal in an inverse manner; and a tuning condenser connected to each of said loops, the constants of said tuning condensers and said loops being so related that each of said loops tunes alike, and said condensers being ganged for operation.

5. In combination, a housing; radio receiving apparatus positioned within said housing and comprising a pair of vacuum tubes, each of said tubes having a cathode and a control electrode, said tubes having a common output circuit; a pair of loops mounted fixedly within said housing at angles to each other and forming at least a portion of the input circuits of said tubes respectively; a pair of impedances connected between said cathodes and a common terminal respectively; a connection from the free terminal of one of said loops to the control electrode of one of said tubes; a connection froin the free terminal of the other of said loops to the control electrode of the other tube; means for connecting the grid return side of said loops to said impedances respectively, said means serving to vary the impedances between said loops and said terminal in an inverse manner; a tuning element in each of said input circuits, the constants of said input circuits being so chosen that each of said input circuits tunes alike, and said elements being ganged for operation.

HENRY C. FORBES. 

